The invention relates to a method for flexible charging of Internet protocol multimedia communication sessions in a network, or a framework of networks, of a multimedia telecommunication system by means of which subscribers communicate and get access to services. It also relates to a telecommunication system including a network or a framework of interlinked and interworking networks sharing common rules and a charging arrangement using control elements including means for generation of charging records related to IP multimedia communication sessions in which these control elements are involved, and to network elements for a telecommunication system comprising a network of interlinked and interworking networks sharing common rules and a charging arrangement using control elements fitted out with means for generation of charging records related to IP multimedia communication sessions.
Use of network resources and services by subscribers in a multimedia telecommunication system, with, for instance, a universal mobile telecommunication system (UMTS) or a non-UMTS next generation network (NGN), will have usually to be accounted, charged and/or billed. This commonly implies the use of charging records (CRs) provided for by means of network entities, or elements, that are directly or indirectly involved in the communication sessions.
It is pointed out here that, even if the known UMTS terminology is used in this application in order to facilitate the understanding of the invention, it must be understood that other systems are also concerned by this invention and particularly the said next generation NGN systems that are now developed. In the same way, reference is made to the known session initiation protocol SIP in the application, but the invention is also relevant to other protocol suites, such as H.323 or BICC used in non-UMTS type of NGN networks.
As known, users in a telecommunication system may be charged for use of resources in different network levels, for instance transport level, service level, content level or else. Charging involves functions that are able to format information related to a chargeable event and transfer it to a charging server to allow a usage determination for which a charged party can be billed. Usually, the billed party is the calling party or a called party admitting such a billing. Pre-paid and post paid-billing are available, they are based on arrangements between subscribers and operators or service providers and they can be based on both on-line and off-line mechanisms. A full control is obtainable when an on-line charging mechanism is used for pre-paid payments.
Charging records CRs, as used in charging mechanisms, can be generated at different network levels according to the needs. Different functions and/or control elements generate different bits of information. For instance, at the service/content level, application servers will generate CRs containing data that relate to what services and contents the application is providing. These CRs can be related to multiple multimedia sessions, if multiple sessions are needed to support an application. At the session level, session control elements will generate CRs containing data related to an IP multimedia session that is controlled by these elements. At the transport level, transport control elements generate CRs containing data related to the usage of transport network resources.
So network entities with CRs providing capabilities in known IP multimedia networks include for instance the following network control elements:
session initiation protocol (SIP) servers, such as serving and proxy call state control function protocol (S and P-CSCF) servers,
application (AS) servers, such as SIP application servers or open service architecture application servers (OSA AS),
entities controlling an interface with an external network, such as break out gateway control function (BGCF), topology-hiding inter-network (THIG) gateways or media gateway control function (MGCF) entities,
transport control entities, including UMTS access network elements such as serving GPRS support node (SGSN) or gateway GPRS support node (GGSN),—with GPRS standing for general packet radio service—.
In NGN networks, IP multimedia network control elements have distributed functions to perform and at least some of these distributed functions have to generate charging records with different bits of information.
The different types of charging records that are produced in relation with a communication session at the different network levels have to be correlated at some point, for instance by a network or service provider, as soon as there is a requirement for accurate charging, accounting and/or billing.
According to a known solution, every charging record contains a correlation identifier (ID) and each identifier is a unique number allowing the network and service providers to correlate the different charging records for a communication session between similar network control elements.
The control over the charging plan is usually performed by the home network of the subscriber that initiated the session. There is almost no flexibility for session control elements, outside the home network of the subscriber initiating the session, to change or update the charging plan during a session in known communication systems. A change could, however, be requested by session control elements in other networks, and particularly by SIP servers in networks other than the home network of the subscriber initiating the session. It could also be requested by session control elements inside user terminals and, for instance, from the called party.
With known systems, there is no possibility to make changes to a charging plan down to a media component level, at any time during the session, by any session control element involved in a session, as it could be appropriate. There is also no possibility to communicate a detailed charging scheme to component level, via session signaling, or to ensure correlation between charging in different network levels up to component level.
If, with known systems, there is a possibility for session control elements, such as end-user terminals, to request changes to the session capabilities via SDP negotiation, and for instance a codec and/or bandwidth change or a media component addition or removal, there is no possibility to indicate, at the same time and via SDP negotiation, how charging can be changed for the different session capabilities negotiated via SDP.